The present invention relates to a novel wear resistant, coated, metal carbide body comprising a metal carbide basic substrate body, a metallic intermediate layer and at least one metal-free hard substance layer. The invention also relates to a method for producing the novel metal carbide body.
German Published Patent Application No. DE-OS 2,528,255 discloses utilitarian and decorative articles that have been coated with hard substances to a thickness of 0.1 to 50 .mu.m, the hard substances being carbides, nitrides, borides, silicides, oxides of elements of Groups III to VI of the Periodic Table, or combinations thereof. DE-OS No. 2,528,255 further proposes to improve the adhesion of the hard substance coatings and to reduce thermal stresses by applying one or a plurality of intermediate layers of metals, alloys of metals and hard substances, or hard substances. The basic substrate materials for these known utilitarian and decorative articles may be metallic or nonmetallic substances, such as steel, castable substances, colored metals, light metals, metal carbides, glass or ceramics.
The known utilitarian and decorative articles may be produced by applying the intermediate and cover layers in succession onto the basic body by gas phase reaction according to the chemical vapor deposition (CVD) process, wherein the layers are precipitated onto the basic body as a result of chemical reactions taking place in the gas phase.
Swiss Pat. No. 542,678 discloses a composite substance for cutting tools. This substance comprises a metallic or nonmetallic substrate, at least one intermediate layer and a wear resistant cover layer, in which the intermediate layer exhibits the following characteristics:
(a) its average hardness lies between the hardness of the substrate and the hardness of the cover layer; PA1 (b) it is more ductile than the cover layer; PA1 (c) its average coefficient of thermal expansion lies between that of the substrate and that of the cover layer; PA1 (d) it is partially dissolved in the substrate as well as in the cover layer; PA1 (e) its average grain size is substantially less than the layer thickness.
The composite substance disclosed in Swiss Pat. No. 542,678 is produced by precipitating the material for the intermediate layer from the gas phase onto the substrate by chemical reaction, with the material of the substrate and the material of the intermediate layer diffusing into one another. The cover layer, in turn, is precipitated from the gas phase onto the intermediate layer, with the material of the cover layer and the material of the intermediate layer diffusing into one another.
It has been found that coated metal carbide bodies comprising a metal carbide basic body, a metallic intermediate layer and at least one metal-free hard substance layer, which are formed through precipitation by chemical reaction from the gas phase as taught in the prior art, have wear characteristics that preclude their use as tools for the machining and shaping by non-cutting means of metal workpieces. My own experiments, for example, have shown that the wear resistance of a titanium nitride layer precipitated from the gas phase onto a metal carbide basic body is reduced by an intermediate layer of nickel, cobalt or titanium, which is likewise precipitated from the gas phase.